The goal of this proposal is to characterize the role of Eph B4 receptors in various stages of angiogenesis. Angiogenesis, new blood vessel growth, is a complex process with a number of guided steps. Within the past decade, numerous growth factors have been shown to direct this process. Recently, Eph B4 receptor knockout mice were shown to die in utero due to cardiovascular defects. However, it is unclear what role this receptor plays in the cardiovascular system. Furthermore, this family of receptor tyrosine kinases has been reported to play significant roles in the retino-tectal systems of the nervous system through repulsion of neurite outgrowth. I would like to determine the role of Eph B4 receptor in the various stages of angiogenesis. Since we have pilot studies indicating phosphorylation of PKB/Akt, we would like to determine if MMP-2 and MMP-9 are increased to allow for endothelial cell movement. PKB/Akt is also implicated in endothelial cell migration. Because PKB/Akt also phosphorylates eNOS to activate nitric oxide, a known mitogen, we will determine if Eph B4 activation results in endothelial cell proliferation. Finally, the role of Eph B4 in tube formation will be investigated. These results from both mesenteric and retinal endothelial cells will greatly increase our understanding of Eph B4 receptor regulation of the various stages of angiogenesis.